How to detect FEC packets ?

[ftv dev]

Is there a fast way to detect if an RTP packet contain a FEC packet or not ?
Do you have any wireshark dissector to analyse FEC headers ?

[Robert Jongbloed]

The first check is ff FEC is operating, it is contained in a "red" packet, that is an RTP packet with redundant data. This is (in webrtc case) indicated via a payload type of 116. Normal VP8 data has a payload type of 100.

This much you can find out from Wireshark.

However, the presence of red packets does not gurantee the presence the redundant "ulpfec" data within it. And unfortunately, as the RTP packet is encrypted it is very difficult to find this out with Wireshark. Even if it could decode the red header, it can't get to it. You would need to decode and parse the packets in a client application to find that out.

Robert Jongbloed
OPAL/OpenH323/PTLib Architect and Co-founder.
Commercial support at http://www.voxlucida.com.au

[ftv dev]

I already knew about abut the first part. However, I didn't read a lot about how the rtp packets are encrypted ( I even forget that and this explain why I didn't succeeded to detect ulpfec packet using wireshark). Instead of parsing from the client, is there a way to disable the encryption ? If this is possible, I think that it will be more efficient to use wireshark. So, what do you think ?

[Vikas]

See issue 491. In chrome dev and canary build you should be able to use the command line flag  --disable-webrtc-encryption to disable webrtc encryption.

/Vikas